The use of partitions can make rolling old data out much easier. Assuming you are using a date based scheme for determining purge dates, by using range partitioning for date based keys you can easily set up a "rolling window" of data.

When the time comes for a purge you split the lead partitions and drop the oldest partitions. No sweat.

However, if a complex set of conditions are required you can consider a compound partitoning scheme, however, these can lead to performance issues.

Another possibility for data that must be maintained is to copy the entire old set of partitions to removable media such as CD-ROM or DVD-R. This allows you to bring it back online as needed by a simple partition add.

Many companies that move a great deal of data at a time such as Choicepoint use this type of technique to add data.

Mike